Lyra and Cathy
Rats are very social and intelligent animals. I have been owned by many rats over the years (currently I am owned by three), and have had lots of firsthand experience. They are always interacting with each other. Whether they are eating, grooming, or sleeping, they do it all together. Their social nature is one of the elements that contributed to the evolution of their complex communication system. Rats are able to communicate very effectively with both audible and ultrasonic squeaks, which are combined with facial signaling.
So, what do rats talk about? Well, the semiotics, “the symbolic sign or value of an acoustic signal”, of rat calls are “usually related to a general situation, condition, or psychological state, rather than to a specific object, feature, or function” (Brudzynski “Principles” 86). These communications lack many of Hockett’s design features of a language, but these intelligent animals are able to understand the semiotic content of these calls and communicate effectively. Rats communicate with vocal signs, and there are a lot of things that they can talk about.
The conversation topics include predators, arrival and departure, emotions, attention calling, and food, as well as others. Some examples include being able to locate other rats, such as a young rat calling for its mother, warn each other of danger, or announce whether they are happy or un-happy. While some calls made by rats have only one meaning, many of their calls are polysemic, allowing for a complex communication system (Brudzynski “Principles”).
The use of ultrasonic communication between rats is a trait most likely selected for because many predators cannot hear ultrasonic noises. This allows rats to communicate secretly, under the radar so to speak. Using ultrasonic communication, rats are able to alert others of a dangerous predator without alerting said predator to their location, or to that of their companions. Ultrasonic communication also comes in handy in keeping the den location secret from predators. Since rats live in communities, all their chatter could attract attention if it was audible. The social aspects of rat communities were also a factor in the development of their communication system. Rats are extremely social animals, with lots to talk about. (Brudzynski “Communications”).
There are two different ultrasonic frequencies used by rats, 22 kHz and 50 kHz. Calls made at the frequency of 22 kHz are made by rats when they are anxious, and feel that they are in danger. These calls are fairly long, usually lasting 300-3400 ms. Rats emit these low frequency ultrasonic calls when a predator is in the vicinity, in order to warn other rats. These calls are also made during confrontations with other rats, or any instance in which a rat feels threatened. While I do not have a bat detector with which I can listen in on the conversations of my rats, judging from their actions, I imagine that my rats make these calls whenever I vacuum. (Brudzynski “Communications”)
When rats are not being threatened by vacuums, or any other predators, they converse on a frequency of 50 kHz. 50 kHz high frequency calls are used in safe, friendly social situations between rats. These calls would be made while rats shared food, groomed each other, or during mating. These calls are also made when rats recognize the scent of another rat that they know, even if the rat in question is not there. The length of these calls is much shorter than the calls made at 22 kHz, lasting only 30-40 milliseconds.
There are two types of calls made by rats at the frequency of 50 kHz. The first calls are of a constant frequency, or flat calls. These calls are made during social interactions in which the rat is not particularly happy, but not in any danger. The rat may be ambivalent to the situation or its companion. The second category of 50 kHz calls are called step-trill calls. These calls are made by happy rats, and are “analogous to human laughter” (Brudzynski “Communications” 47). Laughter, something that seems so human, is practiced by rats as well.
Not only are these social ultrasonic calls made during rat to rat communications, but rats use them with people too! During safe interactions with humans, such as playing, grooming, or feeding, rats emit squeaks at the frequency of 50 kHz. (Brudzynski “Communications” ). These calls made to humans are the same as those made to other rats. I can just imagine what my rats say about me when I bring them lima beans, when they asked for cream cheese.
Rats also use audible calls to communicate. Audible squeaks are made by rats when they are in pain. However, there are some other instances in which they are used. They can also occur when a rat is surprised. More commonly, audible calls are used when submissive rats are dominated by other rats. These calls by submissive rats can occur during serious confrontations, or during play confrontations (Brudzynski “Communications”).
Facial interactions also play an important part during rat communication. Facial interactions, or facial signaling, is a combination of many factors. Rats use their whiskers, secretions of pheromones from glands in their cheeks, movement of the ears, and smell when engaging in this form of communication. Whiskers are very important in introductions to new rats and aggressive behavior between rats. The smell component of facial interactions is a key element when rats are communicating about food. These facial interactions can also be accompanied by biting, or a type of shoving that resembles body-slamming. These actions can be signs of aggressive behavior, but are often used when rats play with each other. Facial interactions are used in combination with ultrasonic and audible calls (Brecht 259).
Lyra and Cathy enjoying a treat.
One instance when rats use facial signaling is when communicating about food (Galaf). I’ll use two of my rats, Cathy and Lyra for an example. If I introduced Kathy to a new food, let’s say, brie, and then return her to her cage where Lyra is waiting, Lyra will interact with Cathy. Using a combination of facial signaling (especially smell) and ultrasonic calls (most likely at 50 kHz, unless Lyra is really upset that she did not get a treat but Cathy did) Lyra will interact with Cathy and become aware of the existence of Brie. If I then took Lyra out of her cage, leaving Cathy inside, and exposed her to a sample of both Brie and Cheddar, she will most likely choose the piece of brie for a snack, because she knows that it is a safe food from her facial interactions with Cathy.
These food conversations can be helpful for rats, but they can also be harmful. Sometimes, these interactions can help rats find new, safe foods. However, researchers are now using these behaviors to kill rats more effectively with poisons. They are using these interactions against rats, hoping that rats that get into poison will come back and interact with others before showing symptoms and dying (Galaf).
Rats have evolved into social, talkative creatures. They use various forms of communications including facial interactions, ultrasonic calls and audible calls. Though their communication does not have all the features of a language, they are able to locate each other, warn each other of danger, talk about food, and even express if they are happy or un-happy. I was already a lover of rats, but I appreciate them even more now that I know the degree to which they communicate, and that they laugh.
Brecht, Michael, and Winrich A Freiwald. "The Many Facets Of Facial Interactions In Mammals." Current Opinion In Neurobiology 22.2 (2012): 259-266. Academic Search Complete. Web. 9 May 2012.
Brudzynski, Stephan. "Communication of Adult Rats by Ultrasonic Vocalization: Biological, Sociobiological, and Neuroscience Approaches." ilar. 50.1 (2009): 43-50. Web. 21 May. 2012.
Brudzynski, Stephan. "Principles of Rat Communication: Quantitative Parameters of Ultrasonic Calls in Rats."Behavior Genetics. 35.1 (2005): 85-92. Web. 25 May. 2012.
Galef Jr., Bennet G. "Norway Rats' Communication About Foods and Feeding Sites." national Wildlife Reeaserch Center Repellents Conference 1995. (1995): 185-201. Web. 25 May. 2012.